The present invention relates to integrated cluster tools used in the processing of semiconductors. More particularly, the present invention relates to a z-axis monitoring apparatus for monitoring the Z-axis position of a wafer support blade on a transfer robot which transfers wafers among multiple chambers in an integrated cluster tool.
In the semiconductor production industry, various processing steps are used to fabricate integrated circuits on a semiconductor wafer. These steps include the deposition of layers of different materials including metallization layers, passivation layers and insulation layers on the wafer substrate, as well as photoresist stripping and sidewall passivation polymer layer removal. In modern memory devices, for example, multiple layers of metal conductors are required for providing a multi-layer metal interconnection structure in defining a circuit on the wafer. Chemical vapor deposition (CVD) processes are widely used to form layers of materials on a semiconductor wafer. Other processing steps in the fabrication of the circuits include formation of a photoresist or other mask such as titanium oxide or silicon oxide, in the form of the desired metal interconnection pattern, using standard lithographic techniques; subjecting the wafer substrate to a dry etching process to remove the conducting layer from the areas not covered by the mask, thereby leaving the metal layer in the form of the masked pattern; removing the mask layer using reactive plasma and chlorine gas, thereby exposing the top surface of the metal interconnect layer; cooling and drying the wafer substrate by applying water and nitrogen gas to the wafer substrate; and removing or stripping polymer residues from the wafer substrate.
CVD processes include thermal deposition processes, in which a gas is reacted with the heated surface of a semiconductor wafer substrate, as well as plasma-enhanced CVD processes, in which a gas is subjected to electromagnetic energy in order to transform the gas into a more reactive plasma. Forming a plasma can lower the temperature required to deposit a layer on the wafer substrate, to increase the rate of layer deposition, or both. However, in plasma process chambers used to carry out these various CVD processes, materials such as polymers are coated onto the chamber walls and other interior chamber components and surfaces during the processes. These polymer coatings frequently generate particles which inadvertently become dislodged from the surfaces and contaminate the wafers.
The chemical vapor deposition, etching and other processes used in the formation of integrated circuits on the wafer substrate are carried out in multiple process chambers. The process chambers are typically arranged in the form of an integrated cluster tool, in which multiple process chambers are disposed around a central transfer chamber equipped with a wafer transport system for transporting the wafers among the multiple process chambers. By eliminating the need to transport the wafers large distances from one chamber to another, cluster tools facilitate integration of the multiple process steps and improve wafer manufacturing throughput.
A typical conventional integrated cluster tool is generally indicated by reference numeral 10 in FIG. 1. An integrated cluster tool 10 such as a Centura HP 5200 tool sold by the Applied Materials Corp. of Santa Clara, Calif., includes one or a pair of adjacent loadlock chambers 12, each of which receives a wafer cassette or holder 13 holding multiple semiconductor wafers 28. The loadlock chambers 12 are flanked by an orientation chamber 14 and a cooldown chamber 16. Multiple process chambers 18 for carrying out various processes in the fabrication of integrated circuits on the wafers 28 are positioned with the orientation chamber 14, the cooldown chamber 16 and the loadlock chambers 12 around a central transfer chamber 20. A transfer robot 22 in the transfer chamber 20 is fitted with a transfer blade 24 which receives and supports the individual wafers 28 from the wafer cassette or holder 13 in the loadlock chamber 12. The transfer robot 22 is capable of rotating the transfer blade 24 in the clockwise or counterclockwise direction in the transfer chamber 20, and the transfer blade 24 can extend or retract to facilitate placement and removal of the wafers 28 in and from the load lock chambers 12, the orientation chamber 14, the cooldown chamber 16 and the process chambers 18.
In operation, the transfer blade 24 initially removes a wafer 28 from the wafer cassette 13 and then inserts the wafer 28 in the orientation chamber 14. The transfer robot 22 then transfers the wafer 28 from the orientation chamber 14 to one or more of the process chambers 18, where the wafer 28 is subjected to a chemical vapor deposition or other process. From the process chamber 18, the transfer robot 22 transfers the wafer 28 to the cooldown chamber 16, and ultimately, back to the wafer cassette or holder 13 in the loadlock chamber 12.
As illustrated in FIG. 2, a standard optical wafer sensor 30 is typically provided on the transfer chamber lid 26 of the transfer chamber 20 and emits a light beam 32 which passes first through a view port (not shown) in the transfer chamber lid 26 and then through an opening 25 in the transfer blade 24 when no wafer is supported on the transfer blade 24, as illustrated. The light is reflected back through the opening 25 to the sensor 30, which transmits a DI signal to the system controller (not shown) to indicate that a wafer is not supported on the transfer blade 24. When a wafer is supported on the transfer blade 24, the light from the sensor 30 is absorbed by the wafer, which covers the opening 25. Consequently, the sensor 30 transmits an appropriate signal to the system controller to indicate the presence of the wafer on the transfer blade 24. The optical wafer sensor 30 typically operates on 24V DC current.
One of the problems associated with the conventional wafer sensor 30 is that the sensor 30 is incapable of detecting the Z-axis position of the transfer blade 24 for accurate insertion and retrieval of the wafers 28 into and out of the wafer cassette 13 in the loadlock chamber 12. The tolerance space between the transfer blade 24 and the wafer cassette 13 in the wafer insertion and retrieval operations is typically about 3 mm. Consequently, distortions in the configuration of the transfer blade 24 due to, for example, heat from the process chambers 18 may cause the transfer blade 24 to exceed the permissible Z-axis tolerance of the transfer blade 24. Consequently, the tilted transfer blade 24 may scratch the wafers upon removal or replacement thereof in the wafer cassette 13, significantly reducing the wafer yield.
Accordingly, an apparatus is needed for monitoring the Z-axis position of a wafer transfer blade on a transfer robot.
An object of the present invention is to provide an apparatus for reducing loss in wafer yield in the processing of wafers in an integrated cluster tool.
Another object of the present invention is to provide an apparatus for preventing scraping of wafers in the removal and insertion of semiconductor wafers from and into a loadlock chamber of an integrated cluster tool due to a distorted transfer blade on a transfer robot.
Still another object of the present invention is to provide an apparatus for monitoring the Z-axis position of a transfer blade on a wafer transfer robot.
Another object of the present invention is to provide an apparatus for detecting and indicating the presence or absence of a wafer on a transfer blade of a wafer transfer robot.
Yet another object of the present invention is to provide an apparatus for facilitating corrective Z-axis positioning of a transfer blade on a wafer transfer robot in order to prevent inadvertent scraping of wafers in the insertion and removal of the wafers into and out of a loadlock chamber.
A still further object of the present invention is to provide a method of enhancing the yield of semiconductor wafers processed in a semiconductor fabrication facility by reducing or preventing inadvertent scraping of the wafers due to distortion of a wafer transfer blade on a transfer robot.
In accordance with these and other objects and advantages, the present invention comprises an apparatus for monitoring the Z-axis position of a transfer blade on a wafer transfer robot which transfers wafers among multiple chambers in a semiconductor fabrication facility. The invention comprises a CCD laser displacement sensor which measures the height or Z-axis position of the transfer blade and generates an analog voltage the value of which depends on the height of the transfer blade. An analog controller connected to the CCD laser displacement sensor converts the analog voltage signal to physical distance, which may be displayed on an LCD display on the analog controller. The analog controller may further be connected to a robot controller through an interface PCB, in which case a voltage signal corresponding to an abnormal position of the transfer blade is transmitted to the robot controller and the wafer transfer operation is terminated.